DESCRIPTION: (Adapted From The Applicant's Abstract.) Communication is the major function of the auditory system in almost all species of higher vertebrates but little is known about the neural processing of communication sounds in any of these species. Mustached bats, Pteronotus parnelli, emit a diverse array of complex communication sounds (calls) as well as highly stereotyped biosonar pulses. Among mammals, the mustached bat's auditory cortex is the best studied and contains several areas that are specialized for processing biosonar information. The processing of calls in its auditory cortex, however, has not been studied at all. The aim of this project is to study the processing of calls in the well developed and highly organized auditory cortex of the mustached bats. This will be accomplished by characterizing single cortical neurons with computer-controlled calls and call components that are shifted in the frequency, intensity and time domains. Cortical specializations for call processing will be explored in terms of facilitation evoked by two or more call components. "Tuning" of call specialized neurons will be measured as a function of parameters of the most effective elements in the calls. These studies will be accompanied by a mapping of the specialized neurons, in any, within each cortical area. Population coding of calls within and among hierarchically equivalent cortical areas will also be tested by correlating a population response vector with a stimulus vector obtained from multiple physical parameters characterizing a call. This project will thus elucidate the common auditory processes that may underlie communication sound processing in all mammals.